System for sound recording



June 2, 1942. v l

B. KREUZER ETA'L sysrEM FOR soUND RECORDING v l'ruled April 2,1546

@EPROM/:Eo LEVEL /N AMPLIFIER I j @www i CmpeEsso/e z @ZZ/WMI 'i @www June 2f 1942. B. KREUZER ETAL SYSTEM FOR souND RECORDING 3 Sheets-Sheet 3 Filed April 2, 1940 BAR ro/v Keel/ZEE www Patented June 2, 1942 SYSTEM FOR SOUND RECORDING Barton Kreuzer, Los

Angeles, Calif., and Hillel ,Y I. Reiskind, Camden, N. J., assignors to Radio Corporation of Ameri aware ca, a corporation of Del- Application April 2, 1940, Serial No. 327,436.v

16 Claims.

This invention relates to sound recording systems and particularly to such systems wherein the signal variations are impressed upon the film asa combination of variable area. and' variable 4intensity variations in a light beam or beams.

These systems also embody noise reduction and `compression. l Variable area sound recording systems, in

I which the sound tracks appear as opaque and transparent longitudinal areas separated'by a .varying trace or traces which correspond to the frequency and amplitude of the signal, are well (Cl. P19-100.3)

and variable area. components with noise reduction and compression.

' Another object of the invention is to record sound having both variable area and variable density components withat least one of said components being nonproportional to the amplitude variations in the original signal.

known, as wellas the variable density type of y system wherein the variations in, frequency and amplitude appear on the sound track as striations of constant width but of varying density.

Noise reduction in the form of a longitudinal opaque section varying in width substantially in accordance with the average amplitude or envelope of the signal is well known for variable area systems, and in the form of vari-ations in the averagedensity of the film in accordance with the averageor envelope amplitude of the signal, is well known for .variable density systems.

In the present invention, the variable area and variable density components are combined in a manner to obtain the optimum signal-tonoise ratio, while the noise reduction action is particularly effective during the silent periods 3 or times of no signal.

The invention may also embody the ,feature of overall compression which has been found to be advantageous in the recording of sound-on-lm for reproduction in various theatres having different acoustic characteristics. pression also aids the recording operators to The use of comproduce a better overall sound track particularly when the amplitude range of the signal is much greater than the film range.

The present linvention will thus produce a combination variable area-variable density sound track having noise reduction andl oompression, the advantages of each"individual feature being retained in the process.

The principal object of the invention, therefore,'is to improve and facilitate the recording of sound-on-lm. Another object of the invention is to obtain an improved sound track record. A further object of theinvention is to record sound having both variable area and variable density components with noise reduction.

Al further object of the invention is'to obtain y impressed upon a compressor 8, and a third por- Another objectof the invention is to produce a sound track having variable area and-variable density components in which the combination of variable area and variable 4density components is not proportional to the variations in the original signal.

Although the novel features which ,are believed to be characteristic of this invention are pointed out with particularity in the claims appended herewith, the manner of its organization and themode of its operation will be better understood by referring to the following description read in conjunction with the accompanying drawings forming a part thereof, in which- FigureV 1 is a diagrammatic drawing of one embodiment of the invention;

Figure 2 is a diagrammatic drawing of a sec-4 ond embodiment of the invention;

Figure 3 is a diagrammatic drawing of a third embodiment of the invention;

Figure 4 is a schematic circuit drawing of a portion of the embodiments shown in Figs. 1,

0 2 and 3;

Figure 5 is a partial view of the appearance f of a sound track made with the recording systems embodying the invention; and

Figures 6, 7, 8, 9, 10 and 11 are graphs illustrating the operation of the systems of Figs. 1, 2 and 3. l

Referring now to Fig. 1, a microphonev 5 feeds a standard amplifier 6, the output'of which is divided, one portion being impressed upon a noise reduction unit 1, another portion being tion upon a monitor amplifier 9, to which is connected a loudspeaker I0. The output of the compressor is impressed upon agalvanometer I2 or other light modulating device, while the output of the noise reduction unit 1 is impressed upon a noise reduction shutter or shutters I4 or other type of noise reduction element. The, output of noise reduction unit I may also be impressed upon the galvanometer i2.

In Fig. 2 another arrangement of the compressor 8 in the system of Fig. 1 is shown wherein the output of amplifier 8 feeds only the compressorB and the monitor amplier 9 with its a sound track combining both variable density loudspeaker l0. In this modification, the Quin booster amplifier from whence it is reflected to put of compressor 8 is impressed upon noise reduction unit 'I for feeding the shutter I4 and also upon -the galvanometer I2.

1n the embodiment of Fig. 3, the output of amplifier 6 is again divided into three portions, one portion feeding the monitor amplifier 9 with its loudspeaker I0, the second portion feeding the compressor 8, and the third second compressor I5, which feeds the regular noise reduction unit I and shutters I4. The out put of compressor 8 is impressed upon the galvanometer I2 in the same manner as shown in Figs. 1 and 2. The details of' the compressor shown at 8 and I5 in Figs. 1, 2 and 3 may be of any standard type, a preferred form being disclosed and claimed in copending application, Serial No. 263,884, filed March 24, 1939.

Referring now to Fig. 4, showing a schematic circuit ofthe noise reduction, portion of the systems shown schematically in Figs. l, 2 and 3, the microphone 5 and amplifier 8 feed the compressor unit 8, as shown in Fig. 1, through a IIV and manual control attenuator I3, the other portion of the output of amplier 6 being impressed upon the noise reduction unit comprising a transformer I'I feeding a rectifier element I8 which is coupled to a, direct current amplifier tube I9 through a filter-timing circuit including resistances 2| and 22 and condenser 23. The bias for the direct current amplifier I9 ls obtained from a variable tap on a resistance 28 shunting a potential source such as a battery 29, while a threshold bias for the rectifier I8 is obtained from a potentiometer 20 shunting a potential source 24. The output of the amplifier I 9 is shown connected through a potential source 3l and an operating coil 32 shunted by a condenser 33 for controlling the separation of a pair of shutters 34. not be employed, depending upon the natural portion feeding al The condenser 33 may or may time constant of the shutter circuit. Connected i in dotted lines across the winding 32 is a coil 62 for actuating a penumbra noise reduction shutter 63, as will be explained hereinafter. Such a penumbra. sound recording system is disclosed and claimed in copending application .Serial No. 265,278, filed March 31, 1939. Although the penumbra coil 62 is shown being operated from the same noise reduction unit feeding the shutter coil 32, the penumbra coil may be separately actuated from a, second noise reduction unit operating in parallel with the one shown.

The shutters 34 are of the noise reduction type employed in the standard variable area sound recording system. -The present system uses these shutters for obtaining the variable area component of the sound track in association with a light source'35, a condenser lens 36, and a mask 31 with a rectangular aperture 38 therein. The light permitted to pass through the aperture 38 is projected upon a mirror 40 of the galvanometer I2 by a lens 4I after passing a fixed penumbra stop 84 and the variable penumbra shutter 63,

ing a narrow elongated slit 43 therein. The light beam appearing on the mask 42 is shown as a rectangular beam graduating in intensity in a direction normal to the slit 43. The light passing the slit 43 is projected upon a sound track portion 45 of a llm 4i by projection lenses 41. The galvanometer mirror 40 is actuated byv a coil 49 fed from the compressorv 8. 'I'he noise reduction unit shown schematically in Fig. 4 may correspond to block 'I in Figs. ,1, 2 and 3, while the shutter 34 may be the shutter block I4, and the a slit mask 42 hav- I noise reduction to permit a small amount of light to pass to the photoelectric cell during the silent portions of' the filmto prevent so-called breath ing during reproduction and to insure the recording of the low modulations. Although there are many salient features provided by compression in sound recording. it could be repeated that compression is desirable from the standpoint of aiding the sound recording operators to obtain an intelligible recording of high momentary signal peaks which otherwise would be beyond the range of the film, 'and to obtain better overall intelligibility wheny the sound tracks are reproduced in theatres having poor acoustic characteristics.

By now referring to the various graphs, the operation of the recording systems shown in Figs. 1, 2 and 3 will be explained. In all these graphs, the dotted lines represent the relationship between the input level or amplitude range of the signal and the reproduced level in db. for the variable density component. The solid line represents the same relationship with respect to the variable area component. The dash-andsingle-dot line shown at 45 in Figs. 6, 7, 8 and 9 represents the overall relationship between input level and reproduced level of the signal, while this line has been placed in Figs. 10 and 1l for purposes of comparison. It will be noted that, in accordance with Fig. 4, the variable area component is produced by the noise reduction shutters 34 varying the dimensions of the light beam, while the variable density component is produced by the vibrations of .the mirror 40 passing varying light densities through the slit 43, variable density noise reduction being simultaneously obtainable by operation of the penumbra shutter 63 if desired either by the same noise reduction unit or by a separate one.

Now, referring to Fig. 6, in which full-track modulation is taken as zero db. and equal to zero db. input level, it will be found that the noise reduction shutters 34 or variable area component follows the envelope of the amplitudes of the input signal in a linear lrelationship to an input level of minus 40 db., while this range of input levels has been compressedv into approximately .l db. of reproduced output for the variable density component. In other words, the variable density component is substantially 100% modulated over the minus 40 to zero input range providing a high signal to noise ratio. 'I'he result of the two components over this important range of input levels is substantially linear, the' amplitude of the variable density component remaining almost constant, while the amplitude oi' the area component controls output volume. At minus 40 db., however, the noise reduction shutters 34 do not respond to further decreases in input level due to the bias placed on the rectifier I8 by potentiometer 20 or by mechanically blocking the shutters 34 at a minimum position, while the variable density component becomes linear or proportional with respect to the variations in inputv level. This condition obtains to 'an input level of approximately minus db., which is probably below ,the lowest level sounds which are suitable for recording, as the ground noise level is generally greater than this signal level. At the minus 40 db. reproduced level, the noise reduction shutters are brought together so that the width of the film zero line or variable area component is approximately 0.7 of a mil in width, which is suiiiciently narrow to obtain optimum `noise reduction. This 0.7 of a mil width is based upon a'. total track width of 70 or 76 mils. It is to be remembered that input levels in the rangebe- Atween minus 80 db.and minus 40 db. are comparatively unimportant with respect to the minus 40 to zero db. range. Thus, over the minus 80 to minus 40 db. range and at times of no signal, the optimuml degree of variable area noise reduction is applied, while the low signal levels of minus 80 db. are expanded to correspond to an output level of minus 40 db., and thus provide a high signal to noise ratio for the density component at these low levels. Furthermore, with the variable density noise reduction elements 62 and 63 simultaneously operating, thev density of the modulated portion as well as the unmodulated portion is increased in the print to further reduce the ground noisein accordance with wellknown practice.

The resulting track is of the formillustrated in Fig. 5, although the lm from a system operating as shown in Fig. 6 will not have the addition of the'narrow-traces 5i and 5l shown at both ends of a modulated portion of the film, but Awill have the constant area and vvariable density modulated portions 52 and 52' of a width comparable to traces l and 5i', as'willbe ex'- plained. Fig. 5 is thusemployed to illustrate the form of track producible by the different arrangements shown in Figs. 1, 2 and 3'as a -simple signal is impressed upon the recording systems. It is difficult to sho'w in a drawing the'variations in the density component of the track, although it is to be noted by referring to Fig'. 6 that the density modulation range between the points 55 and 56 and points'55' and 58' represents an input level range of between minus 40 and minus 80 db., which corresponds to a reproduced range of from minus 40 to zero db. In this range of minus 40 `to minus 80 db. input levels, the width of the sound track remains constant, while the variable density modulations are directly proportional to the variationsV ini input signal. It is also to be noted that, sincethe vcompressor circuit only feeds the galvanometer, the boosterampliiler Il and attenuator i3 (see Fig. 4) may be adjusted so that the low level range from minus 80 db. to minus 40 db. is amplified to a reproduced level of raised approximately db. in level to obtain substantially 100% variable density modulation at the minus 40 db. level and a high signal-tonoiseratio at all amplitudes. From the range of minus 40 db. to zero db. of input level, the variable density component remains substantially constant at 100% modulation, and the track varies only as to its ,area component, and that in a linear manner. It is to be noted that the variable area modulated portion .53 (see Fig. 5) between points 'and 55 is shorter between point 55 and point '51 than `between point 51 and lower point 55'. This is produced by the timing action of the elements 2|, 22 land 23 in the output circuit of rectifier I8 (see Fig. 4). Thus, in the system just described, the .advantages of variable density and variable area recording are combined along with the, advantages of noise reduction. Although the area and density components have a certain relationship in Fig. 6, it is to be understood that this relationship may be reversed. Also, the particular values oi'linput signal and output levels given are illustrative of a preferred form of variation and other ratios of compression as well as other ranges of levels are within the scope of the invention.

minus 40 db. to substantially zero' db. before the nonlinear relationship obtains. This feature permits the obtaining cfa high signal-to-noise ratio at the low signal amplitudes for the variable density component, while utilizing the intrinsic -qualities of variable density recording. Furthermore, by connecting the dotted elements B2 and G3 into the circuit of Fig. 4, variable density noise reduction maybe simultaneously applied -as disclosed in the `above-mentioned copending application Serial No. 265,278. If the density noise 'reduction elements are actuated by a separate noise reductionunit, the variable density noise reduction action may be applied only at the lower input levels. .Also, variable density noisereduction may be applied by applying the output of tube I! to a bias winding on the galvanometer, as disclosed and claimed in copending application Serial No. 311,638., filed December 29, 1939.

Thus. as the signal comes onto the recording system, the variable area component remains ,constant over the minus 80 db. to minus 40 db. range, while the variable density component is Referring now to Fig. 7, the same general type of operation is illustrated, but one which will b e produced by the arrangement of the com# pressor and noise reduction units as shown in Fig.2. In this case,A the Icompressor operates both the variable density and variable area components. Specifically, an `input level range be-` tween zero. and minus 40 db. is compressed into a reproduced level range'of between zero and minus 20` db. for both components, and the addition of both these reproduced levels will produce' an output which will be proportional to the input variations'.v in amplitude. noted in -the operation of Fig. 2 that, at minus 40 db., the variable area component becomes constant, which corresponds to the section between the points 55 and 56 in Fig. 5. Also, at the point of minus 40 db. input level in Fig. 7, the variable density component becomes linear so that the vreproduced output is proportional to the recorded input below this level. By adjustment of the noise reduction circuit, the variable area component becomes constant at a minus 20 db. output level, which corresponds to approximately a 7 mil width of track. In Fig. 6, the operation is such that the areacomponent is reduced to minus 40 db. or a 0.7 mil width. As the 0.7 mil width is preferred for periods of no signal. the area component may be reduced to this width by use of the noise reduction 'circuit shown in copending application Serial'No. 270,876, tiled yApril 29, 1939, in which bucking voltages are produced at predetermined signal levels. Such a circuit will provide a rapid action for low level signals so that as the input signal approaches minus db., the shutters Il (or penumbra shutter 63) will quickly come together to reduce the track tothe .7 mil width, as shown in Fig. 7. By use of the parallel arrangement of rectitlers, the shutters will be held fixed over a predetermined range 'of levels, while the shutters may be given minimum position of separation by a separationV block -placed therebetween. Thus. as in Fig. 6, the

variable area component is reduced to the desired optimum width in the neighborhood o! minus 80 db. This rio-signal condition is illustrated in mail', while/m ng. s, the constant area variable density modulated ble width t0 lines il It will be andA 5|. It will beI noted in Fig. 7 that the variable density component of minus 80 db. corresponds to a reproduced level in the neighborhood of minus 60 db. so the booster amplifier Il and attenuator I3 will be adjusted differently to produce the results shown in Figs. 6 and 7.

Referring Vnow to Fig. 8, this graph represents the operation of the arrangement shown in Fig. 3, wherein a diierent compression rate is applied to the variable density component than to the variable area component, the combination of both, however, producing alinear relationship between the input level and the reproduced level. In this system, a range of zero to minus 40 db. is compressed into a range of zero to minus 10 db. for the variable density component, while the variable area component is the reciprocal thereof and has an input range of zero to minus 40 db. compressed into a reproduced range of zero to minus 30 db. At minus 40 db. input level, the variable area component remains constant, while the variable density component becomes linear with respect to input level, while in the neighborhood of minu's 80 db.

the area component is reduced to a .7 mil width to reduce ground noise at no-signal periods in thevsame manner as in Fig. 7. Also, the attenuator is adjusted to boost the minus 80 db. input level to a minus 50 db. output level providing a high signal-to-noise ratio for low amplitude signals.

Referring now to Fig.' 9, another modification of the operation of the system of Fig. 3 is shown, wherein the variable area component of the sound track has an input level range of zero to minus 40 db. compressed into a range of zero to minus 10 db. output level, while the variable densitypomponent has a range of zero to minus 40 db. compressed into an output range of zero to minus 30 db. At minus 40 db. input level, the variable area component remains constant, while the variable density component varies linearly between the input and output levels. In this figure, it is also to be noted that the variable area component is reduced to the .7 mil width in the neighborhood` ofgr'ninus 80 db. input level. By the use of two compressors, it is obvious that any desired combination' of compression ratios is obtainable.

Inv the operation of the systems shown in Figs.V

l, 2 and 3 and illustrated in the graphs of Figs. 6,

' 7, 8 and 9, the overall relationship between signal input level and output or reproduced level is strictly linear or proportional even though compression is used for one or` both components. These variable compression rates and variable break-away points are easily obtainable with thecircuit disclosed and claimed in the above`v mentioned copending application, Serial No.

, 263,884. Now,l in Figs.v 410 and 11, it is shown wherein the systems of Figs. .1, 2 and 3 may be operated to obtain an overall compression. In

' other words, compression or expansion may be added to a sound track` having the advantages of variable areav and variabledensity recording with noise reduction.

Referring now to Fig. 10, it will be noted that the variable density component has a linear compression over a range of zero to minus 80 db. input level which corresponds to arange of zero to minus 40 db. reproduced level.' A similar compression exists for the variable area component, but the compression rate varies over this range such that a range of .minus 35 db. to zero input level is compressed into a 10 dbarange 20 db. of output level. Thus, the overall relationship between the input signal and a reproduced level will correspondl to the dash-anddouble-dot line shown in this ilgure.

Fig. 11 is a graph representing the operation of a system providing the same overall results of Fig. 10 except that the variable area and variable vdensity compressors are reversed in their operation. It will be noted that in both Figs. 10 and 11the noesignal noise reduction action of the variable area component is present to reduce the width of the track to .7 mil during the no-signal periods. Although a compression action has been shown in Figs. 10 and 11, it is to be understood that expansion is readily obtainable by reversing the action of the compressor. Although Figs. l0 and 11 show results obtainable with the circuit arrangement of Fig. 3, overall compression and expansion are also obtainable with the arrangements of Figs. l and 2. Furthermore,

the compression ratio curves may be of any desired shape, such as both constant, both variable, or one constant and the other variable as shown in Figs. 10 and ll.

Thus, with the above invention, the original input signal may be varied to enable a larger range to be recorded in the sound track area while obtaining the advantages of variable density and variable area recording, noise reduction and compression. It has been found that various types of signals are more suited to one or the other form of recording so that now the recorder operator may adjust his apparatus to choose the best recording conditions for a certain type of signal after he has determined its type during rehearsal or otherwise.

We claim as our invention:

1. A sound recording system comprising a signal source, a light source, means for modulating the intensity of the light from said source in accordance with the instantaneous amplitudes of the signal from said source, means for modulating said light in accordance with the average value of the amplitudes of said signal, and means for varying the rates of modulation of said light by said respective means in accordance with the range of amplitudes being recorded, said average value modulating means remaining ineffective over a certain portion of saidlrange of am/ plitudes.

2. A sound recording system in accordance with claim 1 which includes means for defining said light into a beam, said average value modulating means varying the size of said beam, and means for maintaining said average value modulating means substantially unresponsive to changes in the average value of the amplitudes of said signal over a predetermined amplitude said predetermined vrange at lone rate and responsive at a diiIerent ratefto said signal amplitude below said predetermined range.

I 4. A sound recording system comprising a source of sound waves, a source of light waves, means for forming said light waves into va deilnite shaped beam, means for varying the shape of said beam by said sound`waves,'means for varying the intensity of said light waves in said beam by said sound waves, means included in said shape varying means ior varying the shape of said beam differently over selective ranges of amplitudes of` said soundwaves, and

means included in said intensity varying means for varying the intensity of said beam differently over selective ranges of amplitudes of said sound waves. 4 5. A sound recording system in accordance with claim 4 in which the combination effect of the variations of shape of said beam and the variation in intensity of said beam over any definite amplitude range is proportional to the modulation component and a variable density variable density 4modulation component over a predetermined width of said record, and a subsaid currents in direct ratio to the variations in said amplitudes over a portion of the range of said amplitudes and in a variable ratio over another range of said amplitudes, andmodulating the area of said light beam in accordance with the average value of said currents in an inverse ratio to the ratio of variations in the intensity modulation o! said light beam.

12. A sound recording system comprising a source of sound waves, means for producing a light beam, means for varying the intensity of said light beam in accordance with the instantaneous values of said'sound waves, said means including means for amplifying and compressing currents representing a predetermined range of amplitudes of said sound waves, means for modulating said light beam in accordance with the average lvalues of the amplitudes of said sound waves, said means including means for rectifying and amplifying currents produced by. said sound waves, and means for varying the dimensions of said light beam, said last-mentioned means varying the dimensions of said light beam in inverse ratio to the variations produced by said intensity varying means, said dimension varying means being substantially inactive over a predetermined range of amplitudes of said sound waves. Y

13. A sound recording system in accordance with claim 12 in which said means for modulating said light beam in accordance with the average values of the amplitudes of said sound waves includes means for varying the average intensity of said light beam in accordance with the average amplitude values of said sound waves.

14. A sound iilm record `having a variable area areaover another'range of recorded sound waves,

stantially constant variable density modulation over another predetermined width of said record. 9. A sound lm recordv in accordance with claim y8 in which said record has a substantially constant average density over the portion there- .of having said variable density modulation.

10. The method of sound' recording comprising ytranslating sound waves into electrical currents,

varying the intensity of alight beam in accordance with the' instantaneous values of said currents, varying the dimensions of said light beam in accordance with the'average value over only' certain amplitudes oi' said currents while maintaining said dim'ensionsconstant over other amplitudes of said currents, and varying the average intensity of said light beam in accordance with the average 'value' of said currents.

1 1. The method of sound `recording comprising translating soundwaves into electrical currents, modulating the'intensity of a light beam in accordance with the instantaneous ampiitudes'of a variable density modulation component over bot-h of said ranges of recorded sound waves, said density 'component being vdirectly proportional to said sound waves over the range of sound waves source of sound waves, means for forming light into a beam, means for varying the dimensions of said beam in accordance with the average values o f the amplitudes of said sound waves,

means forvarying the intensity of said beam in accordance with the instantaneous values of said sound waves, and means for reducing the dimensions ofsaid beam to a predetermined `minimum during times of no sound waves and dur d ing times saidv sound waves have low amplitudes.

BARTON KREUZER.

`HIIIIILELI.REISKIND. f 

